Optical encoder with reduced reflected light error having a light non-transparent portion with inclined surfaces

ABSTRACT

In an optical encoder comprising an optical scale in which a light transmission portion and a light non-transparent portion are arranged and an output pattern obtained by emitting an incident light functions as an optical code, a light source portion and a light detecting portion, the light non-transparent portion is constituted of at least one pair of inclined surfaces which are opposed in such a manner as to become farther away from each other towards the side where the incident light enters and set so that an incident angle of the optical axis of the incident light from the light source should not be smaller than a critical angle of incidence, and the light non-transparent portion is constructed so that the incident light which enters one inclined surface should be totally reflected thereon to enter the other inclined surface and then at least part of the incident light should be reflected on the other inclined surface, and a reflected light which is reflected on the other inclined surface should not enter a light emitting portion of the light source and a reflecting portion around the light emitting portion.

TECHNICAL FIELD

The present invention relates to an optical encoder comprising anoptical scale, and more particularly to reduction of detection error.

BACKGROUND ART

An optical encoder, generally, detects a rotation angle of an rotationaxis, a rotation speed and a position and a speed of a linearly-movingobject by emitting parallel beams of light from a light source to anoptical scale having light transmission portions and lightnon-transparent portions which are alternately arranged, converting thelight into a modulation signal and further converting the modulationsignal into an electrical signal with a light detecting element.

An exemplary optical encoder of the background art having a purpose oflower cost and higher precision is disclosed in, for example, PatentDocument 1. In Patent Document 1, it is described that a conventionaltechnique has a problem of high cost since an optical scale ismanufactured through pattern formation “by chromium evaporation of aglass plate and etching of the chromium layer to make a transparentportion and an opaque portion”, and in order to solve this problem, alight shielding portion (a light non-transparent portion) is provided byadditionally forming an inclined portion between light transmissionportions by e.g., resin molding so that an incident angle of an incidentray of light is not smaller than a critical angle and the lightshielding portions and the light transmission portions are alternatelyarranged to make an optical scale like a slit row made by chromiumevaporation, which achieves lower cost through resin molding. Indescription on FIG. 2 showing one preferred embodiment of PatentDocument 1, it is discussed that “it is set that the critical angle is45 degrees or less, the angle made by extensions of inclined surfacessuch as 10a and 10b which constitute one convex portion of an opticalgrating is 90 degrees, an incident angle of light entering the inclinedsurfaces 10a and 10b is 45 degrees and an incident angle of lightentering flat surfaces such as 9a and 9b is 0 degree”, and “the incidentlight on the inclined surface 10a which has an incident angle of 45degrees is totally reflected by 90 degrees to enter the other inclinedsurface 10b at the angle of 45 degrees and then is totally reflectedthereon by 90 degrees, going back to the incident side.”

Among other background-art cases are Patent Documents 2 and 3.

Patent Document 2, for example, shows an optical scale in which lighttransmission portions and light non-transparent portions each of whichis constituted of inclined surfaces which are set so that an incidentangle of an incident light is not smaller than a critical angle arealternately arranged on a surface of a transparent member formed ofpolycarbonate, and it is discussed in the document that since a range ofincident angle of total reflection is wide when a polycarbonate is used,even if the incident light obliquely enters the optical scale, there ishigh probability that the light should be totally reflected to go backto the former side and therefore it is unlikely to cause stray light.

In Patent Document 3, it is discussed that an optical path changingfunction has a shape with projections or depressions which aresufficiently smaller as compared with the thickness of a movable codeplate and at least one shape with projections or depressions is formedin at least one of the aforementioned regions, and providing a pluralityof structures with projections or depressions suppress the thickness ofthe structures with projections or depressions.

Patent Document 1: Japanese Patent Application Laid Open Gazette No.60-140119 (pp. 1 to 2, FIGS. 1 and 2)

Patent Document 2: Japanese Patent Application Laid Open Gazette No.62-5131 (pp. 1 to 3, FIGS. 1 to 3, and 5)

Patent Document 3: Japanese Patent Application Laid Open Gazette No.11-287671 (page 4, FIGS. 1 to 3)

DISCLOSURE OF INVENTION

Problem to be Solved by the Invention

Since the background-art optical encoder is constructed as above, thereis the following problem.

In a case where light which enters the light shielding portion of theoptical scale in which adjacent inclined surfaces make an angle of 90degrees is totally reflected and goes back to the incident side, lightloss caused by the reflection should be ideally zero and the directionof reflection should be completely parallel with an incident lightvector. In other words, this reflected light reversely traces anincident light locus and reaches the light source. Since the angle madeby the above-discussed inclined surfaces, however, is slightly out of 90degrees in many cases, depending on molding precision, there is highprobability that the reflected light which reaches the light sourceenters a portion which can optically function as a reflection film suchas an electrode or a die pad of a light source element. When a reflectedray of light from the light shielding portion in the optical scaleenters the reflection film, the reflected light is further reflectedwith the normal of the reflection film which is drawn from the incidentposition as a symmetry axis.

Usually, an optical scale consists of a plurality of tracks and lightbeams emitted from the light source are converted into substantiallyparallel rays of light by a lens or the like and applied to a pluralityof tracks. In other words, the light source is placed at the substantialcenter of the width occupied by a plurality of tracks.

Therefore, the ray of light reflected on the scale light shieldingportion in one track (temporally, referred to as “a first track”) isfurther reflected on the reflection film and enters another track(temporally, referred to as “a second track”) present at a symmetricalposition with respect to the normal of the reflection film.

Since the amount of light of the beam incident on the symmetricalposition is modulated depending on a scale pattern of the first track,the light modulated in the first track is superimposed on a lightdetecting element which originally receives a transmission lightmodulated by the optical scale in the second track. At this time, amodulation signal of the reflected light from the first track is anantiphase of a modulation signal of the transmission light through thefirst track. The modulation signal of the reflected light from the firsttrack causes an error of detection in the second track.

The same phenomenon as above occurs on the reflected light from thescale light shielding portion in the second track and this causes anerror of detection in the first track.

Even in the case where there is only one track, likewise, the reflectedlight from the track sometimes causes a detection error.

As discussed above, in the optical scale comprising a light shieldingportion in which adjacent inclined surfaces make an angle of 90 degrees,part of light beams entering the optical scale, which enters the lightshielding portion, becomes a reflected light, going the way reverse tothe incident direction, and the incident direction and the reflectiondirection are almost parallel with each other.

If the optical axis of the incident light is almost perpendicular to theoptical scale, the same applies to an optical scale having a transparentportion (which corresponds to the light transmission portion) and anopaque portion (which corresponds to the light shielding portion) whichare formed on a transparent substrate such as a glass by chromiumevaporation and etching. In other words, when part of light beamsincident on one track is reflected on the light shielding portionvapor-deposited with chromium to enter an electrode or a die pad aroundthe light emitting point and is further reflected thereon, there is apossibility that the light enters another track to cause a detectionerror like in the above background-art case.

Patent Documents 1 to 3 do neither disclose nor suggest that thereflected light from the light shielding portion (light non-transparentportion) should cause an error as discussed above.

The present invention is intended to solve the above conventionalproblem and it is an object of the present invention to provide anoptical encoder capable of suppressing a detection error caused byreentrance of a ray of light reflected on a light non-transparentportion of an optical scale into an other track or an original track.

Means for Solving the Problem

According to an aspect of the present invention, an optical encoderincludes an optical scale in which a light transmission portion formedof a flat surface and a light non-transparent portion formed of inclinedsurfaces are arranged and an output pattern obtained by emitting anincident light functions as an optical code, a light source portionincluding at least one light source for emitting the incident light, anda light detecting portion including at least one light detecting elementfor detecting the output pattern, and in the optical encoder, the lightnon-transparent portion is constituted of at least one pair of inclinedsurfaces which are opposed in such a manner as to become farther awayfrom each other towards the side where the incident light enters and setso that an incident angle of the optical axis of the incident light fromthe light source is not smaller than a critical angle of incidence, andthe light non-transparent portion is constructed so that the incidentlight which enters one of the inclined surfaces is totally reflectedthereon to enter the other inclined surface and then at least part ofthe incident light is reflected on the other inclined surface, and areflected light which is reflected on the other inclined surface doesnot enter a light emitting portion of the light source and a reflectingportion around the light emitting portion.

According to another aspect of the present invention, an optical encoderincludes an optical scale in which a light transmission portion and alight non-transparent portion are arranged and an output patternobtained by emitting an incident light functions as an optical code, alight source portion including at least one light source for emittingthe incident light, and a light detecting portion including at least onelight detecting element for detecting the output pattern, and in theoptical encoder, a reflecting portion around a light emitting portion inthe light source is covered with an anti-reflection film.

According to still another aspect of the present invention, an opticalencoder includes an optical scale in which a light transmission portionand a light non-transparent portion are arranged and an output patternobtained by emitting an incident light functions as an optical code, alight source portion including at least one light source for emittingthe incident light, and a light detecting portion including at least onelight detecting element for receiving the output pattern, and in theoptical encoder, the light source is joined onto a die pad on asubstrate and an area of the die pad is almost equal to an area ofcontact between the die pad and the light source.

According to yet another aspect of the present invention, an opticalencoder includes an optical scale having at least one track in which alight transmission portion and a light non-transparent portion arearranged, where an output pattern obtained by emitting an incident lightfunctions as an optical code, a light source portion including at leastone light source for emitting the incident light, and a light detectingportion including at least one light detecting element for receiving theoutput pattern, and in the optical encoder, a portion of the opticalscale which has no track is placed at a position symmetrical to thelight non-transparent portion within an irradiation region of theincident light from the light source with respect to an optical axis ofthe light source as a symmetry axis.

Effects of Invention

In the present invention, since the light non-transparent portion isconstituted of at least one pair of inclined surfaces which are opposedin such a manner as to become farther away from each other towards theside where the incident light enters and set so that the incident angleof the optical axis of the incident light from the light source is notsmaller than the critical angle of incidence, and the lightnon-transparent portion is constructed so that the incident light whichenters one of the inclined surfaces is totally reflected thereon toenter the other inclined surface and then at least part of the incidentlight is reflected on the other inclined surface, and the reflectedlight which is reflected on the other inclined surface does not enterthe light emitting portion of the light source and the reflectingportion around the light emitting portion, the reflected light from thelight non-transparent portion in one track on the optical scale does notenter the reflecting portion around the light emitting portion in thelight source but is absorbed or scattered therein, and therefore thereflected light hardly reenters an other track nor the original track.As a result, it is possible to suppress an error caused by reentrance ofthe ray of light reflected on the light non-transparent portion into another track or the original track.

Further, since the reflecting portion around the light emitting portionin the light source is covered with the anti-reflection film, even if areflected light from the light non-transparent portion in one track onthe optical scale enters the reflecting portion around the lightemitting portion in the light source, the reflected light is absorbed bythe anti-reflection film and therefore the reflected light hardlyreenters an other track or the original track. As a result, it ispossible to suppress an error caused by reentrance of the ray of lightreflected on the light non-transparent portion into an other track orthe original track.

Furthermore, since the light source is joined onto the die pad on thesubstrate and the area of the die pad is almost equal to the area ofcontact between the die pad and the light source, the probability that areflected light from the light non-transparent portion in one track onthe optical scale should enter the die pad serving as the reflectingportion around light emitting portion in the light source becomes lowerand the reflected light hardly reenters an other track or the originaltrack. As a result, it is possible to suppress an error caused byreentrance of the ray of light reflected on the light non-transparentportion into an other track or the original track.

Moreover, since a portion of the optical scale which has no track isplaced at a position symmetrical to the light non-transparent portionwithin the irradiation region of the incident light from the lightsource with respect to the optical axis of the light source as asymmetry axis, even if the incident light from the light source isreflected on the light non-transparent portion to become a reflectedlight and is reflected again on the reflecting portion around lightemitting portion in the light source to enter the optical scale again,the reflected light hardly reenters an other track or the originaltrack. As a result, it is possible to suppress an error caused byreentrance of the ray of light reflected on the light non-transparentportion into an other track or the original track.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1A, 1B and 1C show a typical construction of a background-artoptical encoder, and FIG. 1A is a cross section showing the opticalencoder taken along a plane including tracks, FIG. 1B is a plan viewshowing a light source portion and FIG. 1C is a cross section showing anoptical scale taken along a plane perpendicular to the section of FIG.1A;

FIGS. 2A and 2B show a construction of an optical encoder in accordancewith a first preferred embodiment of the present invention, and FIG. 2Ais a cross section showing the whole construction and FIG. 2B is anenlarged cross section showing part of the construction shown in FIG.2A;

FIGS. 3A and 3B show the optical encoder in accordance with the firstpreferred embodiment of the present invention, and FIG. 3A is a planview viewed from a light detecting portion and FIG. 3B is an enlargedplan view showing part of the construction shown in FIG. 3A;

FIGS. 4A and 4B show another construction of the optical encoder inaccordance with the first preferred embodiment of the present invention,and FIG. 4A is a plan view viewed from the light detecting portion andFIG. 4B is an enlarged plan view showing part of the construction shownin FIG. 4A;

FIGS. 5A and 5B show still another construction of the optical encoderin accordance with the first preferred embodiment of the presentinvention, and FIG. 5A is a plan view viewed from the light detectingportion and FIG. 5B is an enlarged plan view showing part of theconstruction shown in FIG. 5A;

FIGS. 6A and 6B show a construction of an optical encoder in accordancewith a second preferred embodiment of the present invention, and FIG. 6Ais a cross section showing the whole construction and FIG. 6B is anenlarged cross section showing part of the construction shown in FIG.6A;

FIGS. 7A and 7B show a construction of an optical encoder in accordancewith a third preferred embodiment of the present invention, and FIG. 7Ais a cross section showing the whole construction and FIG. 7B is anenlarged cross section showing part of the construction shown in FIG.7A;

FIG. 8 is a cross section showing a construction of an optical encoderin accordance with a fourth preferred embodiment of the presentinvention;

FIGS. 9A and 9B show a construction of an optical encoder in accordancewith a fifth preferred embodiment of the present invention, and FIG. 9Ais a cross section showing the whole construction and FIG. 9B is anenlarged cross section showing part of the construction shown in FIG.9A;

FIGS. 10A and 10B show a construction of an optical encoder inaccordance with a sixth preferred embodiment of the present invention,and FIG. 10A is a cross section showing the whole construction and FIG.10B is an enlarged cross section showing part of the construction shownin FIG. 10A;

FIG. 11 is a plan view showing a principal part of an optical encoder inaccordance with an eighth preferred embodiment of the present invention;

FIG. 12 is a plan view showing a principal part of an optical encoder inaccordance with a ninth preferred embodiment of the present invention;

FIG. 13 is a cross section showing a construction of an optical encoderin accordance with a tenth preferred embodiment of the presentinvention; and

FIGS. 14A and 14B show a construction of the optical encoder inaccordance with the tenth preferred embodiment of the present invention,and FIG. 14A is a plan view viewed from the light detecting portion andFIG. 14B is an enlarged plan view showing part of the construction shownin FIG. 14A.

DESCRIPTION OF REFERENCE SIGNS

1, 101 light source, 2, 116 substrate, 3, 110 die pad, 4, 103 incidentlight, 5, 104 lens, 6 optical axis of outgoing light from the lightsource 1, 7 optical scale, 8, 12, 107 V-shaped projection, 13trapezoidal projection, 8 a, 8 b, 12 a, 12 b, 13 a, 13 b inclinedsurface, 9 flat portion, 10, 108 reflected light, 11 light detectingportion, 11 a light detecting element, 14, 15, 113, 117 track, 19, 109electrode, 20, 102 light emitting point, 21 metal wire, 22anti-reflection film

BEST MODE FOR CARRYING OUT THE INVENTION The First Preferred Embodiment

Prior to discussion on the preferred embodiment, first, discussion willbe made on an error caused by reentrance of a ray of light reflected onthe light non-transparent portion in the optical scale into an othertrack or the original track in the background-art optical encoder shownin Patent Documents 1 to 3, referring to figures. FIGS. 1A, 1B and 1Cshow a typical construction of the above background-art optical encoder,and more specifically, FIG. 1A is a cross section showing the opticalencoder taken along a plane including tracks, FIG. 1B is a plan viewshowing a light source portion, which is viewed from the side of theoptical scale and FIG. 1C is a cross section showing the optical scaletaken along a plane perpendicular to the section of FIG. 1A.

As shown in FIGS. 1A and 1B, a ray of light 103 emitted from a lightemitting point 102 of a light emitting element (light source) 101 suchas an LED provided on a substrate 116 is changed into one of parallelbeams by a lens 104 and enters a track 106 constituted of lighttransmission portions and light shielding portions (lightnon-transparent portions) in an optical scale 105. As shown in FIG. 1C,the track 106 is constituted of V-shaped projections 107 (whichcorrespond to inclined surfaces serving as the light non-transparentportions) and flat portions (which correspond to flat surfaces servingas the light transmission portions) and the design value of a vertexangle of the V-shaped projection 107 is 90 degrees. The refractive indexof the optical scale 105 is selected so that the critical angle whichdepends on the difference in refractive index between it and aperipheral portion such as air should be 45 degrees or less.

Since part of the rays of light (incident light) 103 entering the track106, which enters the V-shaped projection 107, enters a slope (inclinedsurface) of the V-shaped projection at an angle of 45 degrees, the lightis totally reflected twice on the slope of the V-shaped projection 107to become a reflected light 108, going the way reverse to the incidentdirection. The reflected light 108 is refracted by the lens 104 to goback to the light emitting element 101 again.

Usually, the vertex angle of the V-shaped projection 107 is slightly outof the design value of 90 degrees or the incident angle of the ray oflight 103 into the V-shaped projection 107 is slightly out of 45 degreesin many cases due to manufacturing error, and therefore part of or mostof the reflected light 108 does not go back to the light emitting point102 but enters an electrode 109 or a die pad 110 therearound. Thoughdiscussion will be made herein on a case where the reflected light 108enters the electrode 109, the same phenomenon occurs also in the casewhere the reflected light 108 enters the die pad 110. In FIG. 1B, foreasy understanding, the electrode 109 and the die pad 110 are hatched.

Since a metal is generally used as a material of the electrode 109 andits reflectance is high, the reflected light 108 is reflected again witha normal 111 of the electrode 109 extending from the incident point onthe electrode 109 as a symmetry axis. After that, the reflected light108 enters the lens 104 and is refracted thereby, and further enters atrack 112 other than the track 106. Since the track 112 is alsoconstituted of the light transmission portions and the light shieldingportions, part of the reflected light 108 passes through the lighttransmission portions in the track 112 and is received by a lightdetecting element 113 provided on a side (the upper side of the opticalscale 105 in FIG. 1A opposite to the light source 1 in the optical scale105.

It is designed that the light passing through the track 106 should bechanged into a modulation signal through a certain intensity modulationby using an arrangement pattern of the light transmission portions andthe light shielding portions. On the other hand, the reflected light 108is subjected to modulation in phase opposite to the above modulationsignal. Therefore, a ray of light 114, which is emitted from the lightemitting element 101 and changed into one of parallel beams by the lens104 to pass through the light transmission portion in the track 112,directly enters the light detecting element 113, and a ray of light 115,which is part of the reflected light 108 modulated in the track 106 tobe opposite in phase to the light passing through the track 106 andpasses through the track 112, also enters the light detecting element113. In other words, when the optical scale 105 moves in a directionperpendicular to the paper in FIG. 1A, the light detecting element 113outputs a signal in which an output to be originally detected whichreflects an arrangement pattern of the light transmission portions inthe track 112 and an output which reflects an arrangement pattern of thelight shielding portions in the track 106 are superimposed to eachother, and therefore a detection error occurs.

Naturally, however, since the reflected light from the light shieldingportion in the track 112 enters the track 106 through the electrode 109or the die pad 110, an output from a light detecting element 117includes a detection error.

FIGS. 2A, 2B and 3A, 3B each show a construction of an optical encoderin accordance with the first preferred embodiment of the presentinvention, and FIG. 2A is a cross section showing the wholeconstruction, FIG. 2B is an enlarged cross section showing the vicinityof the V-shaped projection (surrounded by a circle) in FIG. 2A, FIG. 3Ais a plan view viewed from a light detecting portion and FIG. 3B is anenlarged plan view showing part (surrounded by a circle) of theconstruction shown in FIG. 3A. FIG. 2A shows a section taken along theline A-A of FIG. 3B.

A light source 1, such as an LED, is placed on a die pad 3 provided on asubstrate 2. As a material of the die pad 3, like that of the electrode,a metal is generally used and its reflectance is high. The substrate 2having a surface in which light is absorbed or scattered and very fewlight is regularly reflected. A light ray (incident light) 4 emittedfrom the light source 1 is so refracted by a lens 5 as to be almostparallel with an optical axis 6. After being refracted by the lens 5,the light ray 4 enters an optical scale 7.

As shown in FIGS. 3A and 3B, the optical scale 7 is constituted of aplurality of tracks 14 and 15 (hatched in FIGS. 3A and 3B) and in eachof the tracks 14 and 15, a plurality of V-shaped projections 8 arealigned with a period of P and a width of P/2. FIGS. 3A and 3B show alinear type scale as an example. The optical scale 7 moves in adirection indicated by the arrow of FIG. 3A relatively to the lightsource 1, the die pad 3 and the lens 5.

The optical scale 7 is constituted of V-shaped projections 8 (each ofwhich corresponds to a light non-transparent portion consisting of atleast one pair of inclined surfaces which are opposed in such a manneras to become farther away from each other towards the side where theincident light 4 enters) and flat portions 9 (each of which correspondsto a light transmission portion formed of a flat surface), and a tiltangle of inclined surfaces 8 a and 8 b of the V-shaped projection 8 is(45−α) degrees with respect to the flat portion 9 (flat surface) asshown in FIG. 2B, where 0<α<45. An angle made by the inclined surfaces 8a and 8 b is (90+2α) degrees, i.e., (90+γ) degrees, where 0<γ<90.

The refractive index of the optical scale 7 is selected so that acritical angle θc which depends on the difference in refractive indexbetween it and a peripheral portion such as air should be smaller than(45−α) degrees. In other words, the light non-transparent portion isconstituted of at least one pair of inclined surfaces 8 a and 8 b whichare opposed in such a manner as to become farther away from each othertowards the side where the incident light 4 enters (the lower side inFIG. 2B) and set so that an incident angle of the optical axis 6 of theincident light 4 from the light source 1 is not smaller than thecritical angle. Therefore, since the light ray 4 entering the V-shapedprojection 8 is totally reflected, the light ray 4 does not enter thelight detecting element 11 a and only the ray of light entering the flatportion 9 and passing therethrough enters the light detecting element 11a in the light detecting portion 11 and detected therein.

Herein, the ratio in width between the flat portion 9 and the V-shapedprojection 8 is not particularly specified and the width of the flatportion 9 is zero in some cases. The light detecting element 11 a is notlimited to a single element but may consist of a plurality of elements.

FIG. 2A shows a case where the light ray 4 going on the left side of theoptical axis 6 enters the right slope (the inclined surface on the rightside) 8 a of the V-shaped projection 8. If the traveling direction ofthe light ray 4 is parallel with the optical axis 6, since the incidentangle is (45−α) degrees, the light ray 4 is totally reflected and entersthe left slope (the inclined surface on the left side) 8 b. Since theincident angle of the light entering the left inclined surface 8 b is(45+3α) degrees, the light ray is totally reflected to become areflected light 10. In this case, the angle made by the travelingdirection of the reflected light 10 and the optical axis 6 is 4α. Sincethe angle made by the inclined surfaces 8 a and 8 b is (90+2α) degrees,in other words, out of 90 degrees, the reflected light 10 is notparallel with the incident light 4.

The reflected light 10 is refracted at a boundary between the opticalscale 7 and the peripheral portion and after the angle made by theoptical axis 6 and the reflected light 10 becomes θ, the reflected light10 is refracted by the lens 5 and reaches the light source portion(substrate 2), but in the optical scale of the first preferredembodiment, α is set so that the reflected light 10 should enter thesubstrate 2 at a position outside the die pad 3 (the reflected light 10should not enter the light emitting portion and a reflecting portionsuch as the die pad 3 or the electrode around the light emitting portionin the light source 1), in other words,x>w  (1)should be satisfied, where x represents a distance between the incidentposition of the reflected light 10 onto the substrate 2 and the lightemitting point of the light source 1 and w represents a distance betweenan end of the die pad 3 and the light emitting point of the light source1.

Though it is assumed in the first preferred embodiment that thesubstrate 2 has a surface in which light is absorbed or scattered andvery few light is regularly reflected, however, if the substrate 2 has ahigh rate of regular reflection like the die pad 3, the above referencesign w represents a distance between an end of a region having a highrate of regular reflection and the light emitting point of the lightsource 1 instead.

In the first preferred embodiment, x can be expressed as:

$\begin{matrix}{x = {( \frac{- {ah}}{f} ) + {( {f - \frac{Lh}{f} + h} ) \times {\tan(\theta)}}}} & (2)\end{matrix}$θ=sin⁻¹(n sin(4α))  (3)

where f represents a focal length of the lens 5, h represents athickness of the light source 1, a represents a distance between theincident position of the light ray 4 onto the optical scale 7 and theoptical axis 6, L represents a distance between a principal plane of thelens and a lower surface of the optical scale 7 and n represents therefractive index of the optical scale 7. Herein, it is assumed that adistance s between the light ray 4 and a reflection point of thereflected light 10 on the left inclined surface 8 b, a distance s2between the reflection point of the reflected light 10 on the leftinclined surface 8 b and an intersection between the reflected light 10and the lower surface of the optical scale 7 and the aberration of thelens 5 are all negligible. Further, the outside of the optical scale 7is assumed to be air having a refractive index of 1.

When tan θ=θ, sin θ=θ, sin(4α)=4α, from Eqs. (1), (2) and (3),

$\begin{matrix}{\alpha > \begin{matrix}\frac{{wf} + {ah}}{4{n( {f^{2} + {hf} - {Lh}} )}} & ({rad})\end{matrix}} & (4)\end{matrix}$

When w=0.5 mm, f=5 mm, h=0.25 mm, a=2 mm, L=5 mm and n=1.5, for example,Eq. (4) is calculated as:α>0.02 (rad)≈1.15 (deg)

In the first preferred embodiment, α is set so that Eq. (4) should besatisfied for a which represents the incident position of the light ray4 with respect to the optical scale 7 in all the cases or most cases. Ifa takes a value ranging from −2 mm to +2 mm, the right side of Eq. (4)takes the maximum value when a=+2 mm, where it is assumed that the leftdirection of FIGS. 2A and 2B is + (positive) with respect to a and othervariables are scalar (positive values having no direction). In the firstpreferred embodiment, α is set not smaller than 1.15 (deg) as above.

Further, the critical angle θc of the optical scale 7 is smaller than(45−α) degrees (θc<45−α) as discussed above. In other words, fromα<45−θc (deg)  (5)and n=1.5, α<3.19 (deg) is satisfied.

Though x and a are expressed by Eqs. (2) and (4), respectively, in thefirst preferred embodiment, the expressions are naturally changed whenthe constitution of the optical system is changed.

It is preferable that the value of the above reference sign α should be3 degrees or less regardless of the critical angle θc of the opticalscale 7. This is intended to reduce the probability that the light ray 4reflected on the right inclined surface 8 a might not enter the leftinclined surface 8 b and go to an unexpected direction, being a straylight.

As discussed above, in the first preferred embodiment, since it isconstructed so that the incident light 4 entering one inclined surface 8a should be totally reflected thereon to enter the other inclinedsurface 8 b and then should be totally reflected on the other inclinedsurface 8 b and the reflected light 10 reflected on the other inclinedsurface 8 b should not enter the light emitting portion and thereflecting portion (such as the electrode of the light source 1 (lightemitting element) or the die pad 3) around the light emitting portion inthe light source 1, and the light ray 10 reflected on the lightnon-transparent portion (V-shaped projection 8) in one track (e.g., thetrack 14) on the optical scale 7 does not enter the reflecting portionsuch as the electrode or the die pad 3 in the light source 1 but isabsorbed or scattered therein, the light ray 10 hardly enters the othertrack (e.g., the track 15) or the original track (e.g., the track 14).As a result, it is possible to suppress a detection error caused byreentrance of the light ray reflected on the light non-transparentportion (the V-shaped projection 8) into the other track or the originaltrack.

The above discussion has been made on the case where it is constructedso that the incident light 4 entering one inclined surface 8 a should betotally reflected to enter the other inclined surface 8 b and should befurther totally reflected on the other inclined surface 8 b. Besides theabove effect, such a construction produces an effect that since theincident light is surely reflected totally on the light non-transparentportion (the inclined surfaces 8 a and 8 b) without being leaked on theside where the light detecting element 11 a is placed, it is possible tosuppress the stray light which is a cause of error. Not only in the casewhere the incident light is totally reflected on the other inclinedsurface 8 b, however, but also in the case where at least part of theincident light is reflected on the other inclined surface 8 b,similarly, with the construction where the reflected light 10 reflectedon the other inclined surface 8 b should not enter the light emittingportion and the reflecting portion (the electrode of the light source 1(light emitting element) and the die pad 3) around the light emittingportion in the light source 1, it is possible to suppress a detectionerror caused by the light ray reflected on the light non-transparentportion (the V-shaped projection 8).

In a case where the light ray 4 enters the optical scale 7, beinginclined at an angle of φ with respect to the optical axis 6, in otherwords, in a case where an angle made by the normal of the flat surface(the flat portion 9) and the optical axis 6 of the incident light 4 fromthe light source 1 is φ, Eq. (3) is changed as follows, where withrespect to φ, the counterclockwise direction is positive with theoptical axis 6 as a reference in FIG. 2A and the others are scalar likein Eq. (3). The following equation can be naturally applied to a casewhere the light ray 4 enters in parallel with the optical axis 6 bysetting that φ=0.θ=|sin⁻¹(n sin(4α−φ))|  (3a)

Further, in all the cases or most cases of a representing the incidentposition of the light ray 4, α is set as follows:(−45+θc+φ)/3<α<45−θc+φ (deg)  (5a)If φ≦4α, in other words, α≧φ/4 is satisfied, α is set so that theconditional expression obtained by substituting Eq. (3a) into Eqs. (2)and (1) and 0<α<45 as well as Eq. (5a) should be satisfied.If φ>4α, in other words, α<φ/4 is satisfied, α is set so that theconditional expression obtained by substituting Eq. (3a) into Eqs. (6)and (1) and 0<α<45 as well as Eq. (5a) should be satisfied.

Though the above discussion has been made on the case where the lightray 4 going on the left side of the optical axis 6 enters the rightinclined surface 8 a of the V-shaped projection 8, if the light ray 4going on the right side of the optical axis 6 enters the left inclinedsurface 8 b of the V-shaped projection 8, the phenomenon symmetrical tothe above case occurs.

Though the above discussion has been made on the case where the opticalscale 7 is a linear type as shown in FIGS. 3A and 3B, the optical scale7 is not limited to this type but may be a rotary type as shown in FIGS.4A, 4B and 5A, 5B and this case also produces the same effect.

FIGS. 4A, 4B and 5A, 5B show one example and another example of theoptical encoder having a rotary type optical scale, respectively, andFIGS. 4A and 5A are plan views viewed from the light detecting portionand FIGS. 4B and 5B are enlarged plan views showing part (surrounded bycircles) of the construction shown in FIGS. 4A and 5A. In FIGS. 4A, 4Band 5A, 5B, the tracks 14 and 15 are hatched.

In FIG. 4B, in each of the tracks 14 and 15, a plurality of V-shapedprojections 8 are arranged with a period of 2φ and a width of φ, and theoptical scale 7 moves in a direction indicated by the arrow of FIG. 4Arelatively to the light source 1, the die pad 3 and the lens 5 (rotatesaround a central axis of the optical scale 7 as a rotation axis).

In FIG. 5B, in each of the tracks 14 and 15, a plurality of V-shapedprojections 8 are arranged and while the tops of the V-shapedprojections 8 in FIG. 4B are extended along a direction of the radius ofthe optical scale 7, the tops of the V-shaped projections 8 of FIG. 5Bare extended along a direction orthogonal to the radius direction of theoptical scale 7 (in parallel with the traveling direction of the opticalscale 7). In each of the tracks 14 and 15, groups each of which consistsof five V-shaped projections 8 are arranged with a period of 2φ and awidth of φ. The optical scale 7 moves in a direction indicated by thearrow of FIG. 5A relatively to the light source 1, the die pad 3 and thelens 5 (rotates around the central axis of the optical scale 7 as arotation axis).

Though FIG. 5B shows the case where five V-shaped projections 8constitute a group, the group is not limited to this but may beconstituted of any number of V-shaped projections 8.

Also in the linear type optical scale 7 of FIG. 3B, the V-shapedprojections 8 may be arranged so that their tops should be placed inparallel with the traveling direction of the optical scale 7.

Though FIGS. 3A, 4A and 5A show the case where two tracks 14 and 15 arearranged, the arrangement of the tracks is not limited to this, and anynumber of tracks may be arranged. The number of tracks may be naturallyone.

The Second Preferred Embodiment

FIGS. 6A and 6B show a construction of an optical encoder in accordancewith the second preferred embodiment of the present invention, and FIG.6A is a cross section showing the whole construction and FIG. 6B is anenlarged cross section showing the vicinity of the V-shaped projection(surrounded by a circle) of the construction shown in FIG. 6A.

While the case where the light ray 4 going on the left side of theoptical axis 6 enters the right inclined surface 8 a of the V-shapedprojection 8 has been discussed in the first preferred embodiment, thecase where the light ray 4 going on the left side of the optical axis 6enters the left inclined surface 8 b of the V-shaped projection 8 willbe discussed in the second preferred embodiment. This case shows aphenomenon symmetrical to the case where the light ray 4 going on theright side of the optical axis 6 enters the right inclined surface 8 aof the V-shaped projection.

Like in the first preferred embodiment, the optical scale 7 isconstituted of the V-shaped projections 8 and the flat portions 9, andthe tilt angle of the inclined surfaces 8 a and 8 b of the V-shapedprojection 8 is (45−α) degrees with respect to the flat portion 9 (flatsurface), where 0<α<45. The angle made by the inclined surfaces 8 a and8 b is (90+2α) degrees, i.e., (90+γ) degrees, where 0<γ<90. Therefractive index of the optical scale 7 is selected so that the criticalangle θc which depends on the difference in refractive index between itand a peripheral portion such as air should be smaller than (45−α)degrees.

As shown in FIG. 6A, when the traveling direction of the light ray 4 isparallel with the optical axis 6, since the incident angle is (45−α)degrees, the light ray 4 is totally reflected and enters the rightinclined surface 8 a. Since the incident angle of the light ray 4 ontothe right inclined surface 8 a is (45+3α) degrees, the light ray 4 isalso totally reflected thereon to become the reflected light 10. At thistime, the angle made by the traveling direction of the reflected light10 and the optical axis 6 is 4α degrees.

The reflected light 10 is refracted at the lower surface of the opticalscale 7 and after the angle made by the optical axis 6 and the reflectedlight 10 becomes θ, the reflected light 10 is refracted by the lens 5and reaches the substrate 2, but like in the first preferred embodiment,α is set so that the reflected light 10 should enter the substrate 2 ata position outside the die pad 3 (the reflected light 10 should notenter the light emitting portion and the reflecting portion such as thedie pad 3 or the electrode around the light emitting portion in thelight source 1).

In the second preferred embodiment, since the direction of the reflectedlight 10 with respect to the optical axis 6 is opposite to that in thefirst preferred embodiment, x can be expressed as follows:

$\begin{matrix}{x = {( \frac{ah}{f} ) + {( {f - \frac{Lh}{f} + h} ) \times {\tan(\theta)}}}} & (6)\end{matrix}$

Herein, it is assumed that a distance s between the light ray 4 and areflection point of the reflected light 10 on the right inclined surface8 a, a distance s2 between the reflection point of the reflected light10 on the right inclined surface 8 a and the intersection between thereflected light 10 and the lower surface of the optical scale 7 and theaberration of the lens 5 are all negligible.

When tan θ=θ, sin θ=θ, sin(4α)=4α, from Eqs. (1), (3) and (6),

$\begin{matrix}{\alpha > \begin{matrix}\frac{{wf} - {ah}}{4{n( {f^{2} + {hf} - {Lh}} )}} & ({rad})\end{matrix}} & (7)\end{matrix}$

When w=0.5 mm, f=5 mm, h=0.25 mm, a=2 mm, L=5 mm and n=1.5, for example,Eq. (7) is calculated as:α>0.013 (rad)≈0.76 (deg)

Though it is also assumed in the second preferred embodiment that thesubstrate 2 has a surface in which light is absorbed or scattered andvery few light is regularly reflected, however, if the substrate 2 has ahigh rate of regular reflection like the die pad 3, the above referencesign w represents a distance between an end of a region having a highrate of regular reflection and the light emitting point of the lightsource 1 instead.

In the second preferred embodiment, α is set so that Eq. (1) should besatisfied for a which represents the incident position of the light ray4 with respect to the optical scale 7 in all the cases or most cases. Ifa takes a value ranging from −2 mm to +2 mm, the value of the right sideof Eq. (7) becomes maximum when a=−2 mm, and like in the first preferredembodiment, the value is;α>0.02 (rad)≈1.15 (deg)where it is assumed that the left direction of FIG. 6A is + (positive)with respect to a and other variables are scalar (positive values havingno direction). In other words, if the light ray 4 enters either theright inclined surface 8 a or the left inclined surface 8 b, α may beset larger than the maximum value in the right side of Eq. (4) or (7)when a is changed.

Further, α is so set as to satisfy Eq. (5), and from n=1.5, α satisfies;α<3.19 (deg)

Though x and a are expressed by Eqs. (6) and (7), respectively, in thesecond preferred embodiment, the expressions are naturally changed whenthe constitution of the optical system is changed.

Like in the first preferred embodiment, it is preferable that the valueof the above reference sign α should be about 3 degrees or lessregardless of the critical angle θc of the optical scale 7. This isintended to reduce the probability that the light ray 4 reflected on theleft inclined surface 8 b might not enter the right inclined surface 8 aand go to an unexpected direction, being a stray light.

As discussed above, in the second preferred embodiment, since it isconstructed so that the incident light 4 entering one inclined surface 8b should be totally reflected thereon to enter the other inclinedsurface 8 a and then should be totally reflected on the other inclinedsurface 8 a and the reflected light 10 reflected on the other inclinedsurface 8 a should not enter the light emitting portion and thereflecting portion (such as the electrode of the light source 1 (lightemitting element) or the die pad 3) around the light emitting portion inthe light source 1, and the light ray 10 reflected on the lightnon-transparent portion (V-shaped projection 8) in one track on theoptical scale 7 does not enter the reflecting portion such as theelectrode or the die pad 3 in the light source 1 but is absorbed orscattered therein, the light ray 10 hardly enters the other track or theoriginal track. As a result, it is possible to suppress a detectionerror caused by reentrance of the light ray 10 reflected on the lightnon-transparent portion (the V-shaped projection 8) into the other trackor the original track.

The above discussion has been made on the case where it is constructedso that the incident light 4 entering one inclined surface 8 b should betotally reflected to enter the other inclined surface 8 a and should befurther totally reflected on the other inclined surface 8 a. Since theincident light is surely reflected totally on the light non-transparentportion (the inclined surfaces 8 a and 8 b) without being leaked on theside where the light detecting element 11 a is placed, this alsoproduces an effect of suppressing the stray light which is a cause oferror. Not only in the case where the incident light is totallyreflected on the other inclined surface 8 a, however, but also in thecase where at least part of the incident light is reflected on the otherinclined surface 8 a, similarly, with the construction where thereflected light 10 reflected on the other inclined surface 8 a shouldnot enter the light emitting portion and the reflecting portion (theelectrode of the light source 1 (light emitting element) and the die pad3) around the light emitting portion in the light source 1, it ispossible to suppress a detection error caused by the light ray 10reflected on the light non-transparent portion (the V-shaped projection8).

In a case where the light ray 4 enters the optical scale 7, beinginclined at an angle of φ with respect to the optical axis 6, in otherwords, in a case where an angle made by the normal of the flat surface(the flat portion 9) and the optical axis 6 of the incident light 4 fromthe light source 1 is φ, Eq. (3) is changed as follows, where withrespect to φ, the counterclockwise direction is positive with theoptical axis 6 as a reference in FIG. 6A and the others are scalar.θ=|sin⁻¹(n sin(4α+φ))|  (3b)

Further, in all the cases or most cases of a representing the incidentposition of the light ray 4, α is set as follows:(−45+θc−φ)/3<α<45−θc−φ (deg)  (5b)If φ≧−4α, in other words, α≧−φ/4 is satisfied, α is set so that theconditional expression obtained by substituting Eq. (3b) into Eqs. (6)and (1) and 0<α<45 as well as Eq. (5b) should be satisfied.If φ>−4α, in other words, α<−φ/4 is satisfied, α is set so that theconditional expression obtained by substituting Eq. (3b) into Eqs. (2)and (1) and 0<α<45 as well as Eq. (5b) should be satisfied.

Though the first and second preferred embodiments show the respectiveranges of design values of α in the case where the light ray 4 entersthe optical scale 7, being inclined at an angle of φ with respect to theoptical axis 6 and the light ray 4 enters the right inclined surface 8 aand the left inclined surface 8 b, in an actual design, a has only to beset so that both conditional ranges of design values shown in the firstand second preferred embodiments should be satisfied.

Needless to say, the optical scale 7 may be either a linear type shownin, e.g., FIG. 3B or a rotary type shown in, e.g., FIGS. 4B and 5B.

The Third Preferred Embodiment

FIGS. 7A and 7B show a construction of an optical encoder in accordancewith the third preferred embodiment of the present invention, and FIG.7A is a cross section showing the whole construction and FIG. 7B is anenlarged cross section showing the vicinity of the V-shaped projection(surrounded by a circle) of the construction shown in FIG. 7A.

While the optical scale 7 is constituted of the V-shaped projections 12and the flat portions 9 like in the first and second preferredembodiments, the tilt angle of the inclined surfaces 12 a and 12 b ofthe V-shaped projection 12 is (45+α) degrees with respect to the flatportion 9 (flat surface), where 0<α<45, unlike in the first and secondpreferred embodiments. Further, the angle made by the inclined surfaces12 a and 12 b is (90−2α) degrees, i.e., (90−γ) degrees, where 0<γ<90.

The refractive index of the optical scale 7 is selected so that thecritical angle θc which depends on the difference in refractive indexbetween it and a peripheral portion such as air should be smaller than(45−3α) degrees. Therefore, since the light ray 4 entering the V-shapedprojection 12 is reflected thereon, the light ray 4 does not enter thelight detecting element 11 but only the light ray 4 entering the flatportion 9 and passing therethrough enters the light detecting element 11to be detected.

FIG. 7B shows a case where the light ray 4 going on the left side of theoptical axis 6 enters the right slope (the inclined surface on the rightside) 12 a of the V-shaped projection 12. If the traveling direction ofthe light ray 4 is parallel with the optical axis 6, since the incidentangle is (45+α) degrees, the light ray 4 is totally reflected and entersthe left slope (the inclined surface on the left side) 12 b. Since theincident angle of the light entering the left inclined surface 12 b is(45−3α) degrees, the light ray is totally reflected to become thereflected light 10. In this case, the angle made by the travelingdirection of the reflected light 10 and the optical axis 6 is 4α. Sincethe angle made by the inclined surfaces 12 a and 12 b is (90−2α)degrees, in other words, out of 90 degrees, the reflected light 10 isnot parallel with the incident light 4.

The reflected light 10 is refracted at a boundary between the opticalscale 7 and the peripheral portion and after the angle made by theoptical axis 6 and the reflected light 10 becomes θ, the reflected light10 is refracted by the lens 5 and reaches the substrate 2, but in thethird preferred embodiment, α is set so that the reflected light 10should enter the substrate 2 at a position outside the die pad 3 (thereflected light 10 should not enter the light emitting portion and thereflecting portion such as the die pad 3 or the electrode around thelight emitting portion in the light source 1), in other words,x>w  (1)should be satisfied, where x represents a distance between the incidentposition of the reflected light 10 onto the substrate 2 and the lightemitting point of the light source 1 and w represents a distance betweenan end of the die pad 3 and the light emitting point of the light source1.

In the third preferred embodiment, like in the second preferredembodiment, x can be expressed as;

$\begin{matrix}{x = {( \frac{ah}{f} ) + {( {f - \frac{Lh}{f} + h} ) \times {\tan(\theta)}}}} & (6)\end{matrix}$θ=sin⁻¹(n sin(4α))  (3)

where f represents a focal length of the lens 5, h represents athickness of the light source 1, a represents a distance between theincident position of the light ray 4 onto the optical scale 7 and theoptical axis 6, L represents a distance between a principal plane of thelens and a lower surface of the optical scale 7 and n represents therefractive index of the optical scale 7. Herein, it is assumed that adistance s between the light ray 4 and a reflection point of thereflected light 10 on the left inclined surface 12 b, a distance s2between the reflection point of the reflected light 10 on the leftinclined surface 12 b and the intersection between the reflected light10 and the lower surface of the optical scale 7 and the aberration ofthe lens 5 are all negligible. Further, the outside of the optical scale7 is assumed to be air having a refractive index of 1.

When tan θ=θ, sin θ=θ, sin(4α)=4α, from Eqs. (1), (3) and (6),

$\begin{matrix}{\alpha > \begin{matrix}\frac{{wf} - {ah}}{4{n( {f^{2} + {hf} - {Lh}} )}} & ({rad})\end{matrix}} & (7)\end{matrix}$

When w=0.5 mm, f=5 mm, h=0.25 mm, a=−2 to +2 mm, L=5 mm and n=1.7, forexample, Eq. (7) is calculated as:α>0.018 (rad)≈1.01 (deg)where the value of the right side of Eq. (7) becomes maximum when a=−2mm, and α is set so that this condition should be satisfied. It isassumed that the left direction of FIG. 7 is + (positive) with respectto a and other variables are scalar (positive values having nodirection). Herein, the refractive index n of the optical scale 7 is1.7, unlike in the first and second preferred embodiments.

Though it is assumed also in the third preferred embodiment that thesubstrate 2 has a surface in which light is absorbed or scattered andvery few light is regularly reflected, however, if the substrate 2 has ahigh rate of regular reflection like the die pad 3, the above referencesign w represents a distance between an end of a region having a highrate of regular reflection and the light emitting point of the lightsource 1 instead.

Further, the critical angle θc of the optical scale 7 is smaller than(45−3α) degrees (θc<45−3α) as discussed above. In other words, fromα<(45−θc)/3 (deg)  (8)and n=1.7, α<2.99 (deg) is satisfied.

Though x and a are expressed by Eqs. (6) and (7), respectively, in thethird preferred embodiment, the expressions are naturally changed whenthe constitution of the optical system is changed.

As discussed above, in the third preferred embodiment, since it isconstructed so that the incident light 4 entering one inclined surface12 a should be totally reflected thereon to enter the other inclinedsurface 12 b and then should be totally reflected on other inclinedsurface 12 b and the reflected light 10 reflected on the other inclinedsurface 12 b should not enter the light emitting portion and thereflecting portion (such as the electrode of the light source 1 (lightemitting element) or the die pad 3) around the light emitting portion inthe light source 1, and the light ray 10 reflected on the lightnon-transparent portion (V-shaped projection 12) in one track on theoptical scale does not enter the reflecting portion such as theelectrode or the die pad 3 in the light source 1 but is absorbed orscattered therein, the light ray 10 hardly enters the other track or theoriginal track. As a result, it is possible to suppress a detectionerror caused by reentrance of the light ray reflected on the lightnon-transparent portion (the V-shaped projection 12) into the othertrack or the original track.

The above discussion has been made on the case where it is constructedso that the incident light 4 entering one inclined surface 12 a shouldbe totally reflected to enter the other inclined surface 12 b and shouldbe further totally reflected on the other inclined surface 12 b. Sincethe incident light is surely reflected totally on the lightnon-transparent portion (the inclined surfaces 12 a and 12 b) withoutbeing leaked on the side where the light detecting element 11 a isplaced, this also produces an effect of suppressing the stray lightwhich is a cause of error. Not only in the case where the incident lightis totally reflected on the other inclined surface 12 b, however, butalso in the case where at least part of the incident light is reflectedon the other inclined surface 12 b, similarly, with the constructionwhere the reflected light 10 reflected on the other inclined surface 12b should not enter the light emitting portion and the reflecting portion(the electrode of the light source 1 (light emitting element) and thedie pad 3) around the light emitting portion in the light source 1, itis possible to suppress a detection error caused by the light rayreflected on the light non-transparent portion (the V-shaped projection12).

In a case where the light ray 4 enters the optical scale 7, beinginclined outward at an angle of φ with respect to the optical axis 6, inother words, in a case where an angle made by the normal of the flatsurface (the flat portion 9) and the optical axis 6 of the incidentlight 4 from the light source 1 is φ, Eq. (3) is changed as follows,like in the second preferred embodiment, where with respect to φ, thecounterclockwise direction is positive with the optical axis 6 as areference in FIG. 7A and the others are scalar like in Eq. (3).θ=|sin⁻¹(n sin(4α+φ))|  (3b)

Further, in all the cases or most cases of a representing the incidentposition of the light ray 4, α is set as follows:−45+θc−φ<α<(45−θc−φ)/3 (deg)  (5c)If φ≧−4α, in other words, α≧−φ/4 is satisfied, α is set so that theconditional expression obtained by substituting Eq. (3b) into Eqs. (6)and (1) and 0<α<45 as well as Eq. (5c) should be satisfied.If φ<−4α, in other words, α<−φ/4 is satisfied, α is set so that theconditional expression obtained by substituting Eq. (3b) into Eqs. (2)and (1) and 0<α<45 as well as Eq. (5c) should be satisfied.

Though the above discussion has been made on the case where the lightray 4 going on the left side of the optical axis 6 enters the rightinclined surface 12 a of the V-shaped projection 12, if the light ray 4going on the right side of the optical axis 6 enters the left inclinedsurface 12 b of the V-shaped projection 12, the phenomenon symmetricalto the above case occurs.

Further, if the light ray 4 going on the left side of the optical axis 6enters the left inclined surface 12 b of the V-shaped projection 12, αis set so that 0<α<45, the conditional expression obtained from Eqs.(1), (2) and (3a) and Eq. (5d) below should be satisfied.45+θc+φ<α<(45−θc+φ)/3 (deg)  (5d)where φ≦4α, in other words, α≧φ/4 is satisfied.If φ>4α, in other words, α<φ/4 is satisfied, α is set so that 0<α<45,the conditional expression obtained from Eqs. (1), (6) and (3a) and Eq.(5d) should be satisfied.

Though the third preferred embodiment shows the respective ranges ofdesign values of α in the case where the light ray 4 enters the opticalscale 7, being inclined at an angle of φ with respect to the opticalaxis 6 and the light ray 4 enters the right inclined surface 8 a and theleft inclined surface 8 b, in an actual design, α is set so that bothconditional ranges of design values shown in the third preferredembodiment should be satisfied.

Needless to say, the optical scale 7 may be either a linear type shownin, e.g., FIG. 3B or a rotary type shown in, e.g., FIGS. 4A, 4B and 5A,5B.

The Fourth Preferred Embodiment

FIG. 8 is a cross section showing a construction of an optical encoderin accordance with the fourth preferred embodiment of the presentinvention. Like in the first and second preferred embodiments, theoptical scale 7 is constituted of the V-shaped projections 8 and theflat portions 9, and the tilt angle of the inclined surfaces 8 a and 8 bof the V-shaped projection 8 is (45−α) degrees with respect to the flatportion 9 (flat surface), where 0<α<45. The angle made by the inclinedsurfaces 8 a and 8 b is (90+2α) degrees, i.e., (90+γ) degrees, where0<γ<90.

The fourth preferred embodiment shows the case where the light ray 4going on the left side of the optical axis 6 enters the left inclinedsurface 8 b.

The refractive index of the optical scale 7 is selected so that thecritical angle θc which depends on the difference in refractive indexbetween the optical scale 7 and a peripheral portion such as air shouldbe smaller than (45−α) degrees.

Further in the fourth preferred embodiment, α is set so that thereflected light 10 within a range of the incident position a of thelight ray 4 onto the optical scale 7 should not enter anywhere within aneffective diameter D of the lens 5.

Specifically, α is set so that;a−L tan θ<−D/2  (9)should be satisfied, where it is assumed that the left direction of FIG.8 is + (positive) with respect to a.

Herein, as shown in FIG. 2B, it is assumed that both a distance sbetween the light ray 4 and the reflection point of the reflected light10 on the right inclined surface 8 a and a distance s2 between thereflection point of the reflected light 10 on the right inclined surface8 a and the intersection between the reflected light 10 and the lowersurface of the optical scale 7 are negligible.

When tan θ=θ, sin θ=θ, sin(4α)=4α, from Eqs. (3) and (9),α>(2a+D)/8nL (rad)  (10)

When a=−D/2 to +D/2, D=2 mm, n=1.5 and L=10 mm, for example, α is set sothat;α>0.03 (rad)≈1.91 (deg)should be satisfied.

Further, α is set so that Eq. (5) should be also satisfied.

From n=1.5, α is set so that;α>3.19 (deg)should be satisfied.

Though α is expressed by Eq. (10) in the fourth preferred embodiment,the expression is naturally changed when the constitution of the opticalsystem is changed.

Like in the first and second preferred embodiments, it is preferablethat the value of the above reference sign a should be about 3 degreesor less regardless of the critical angle θc of the optical scale 7. Thisis intended to reduce the probability that the light ray 4 reflected onthe left inclined surface 8 b might not enter the right inclined surface8 a and go to an unexpected direction, being a stray light.

As discussed above, in the fourth preferred embodiment, since it isconstructed so that the incident light 4 entering one inclined surface 8b should be totally reflected thereon to enter the other inclinedsurface 8 a and then should be totally reflected on the other inclinedsurface 8 a and the reflected light 10 reflected on the other inclinedsurface 8 a should not enter the light emitting portion and thereflecting portion (such as the electrode of the light source 1 (lightemitting element) or the die pad 3) around the light emitting portion inthe light source 1, and the light ray 10 reflected on the lightnon-transparent portion (V-shaped projection 8) in one track on theoptical scale 7 does not enter the reflecting portion such as theelectrode or the die pad 3 in the light source 1, the light ray 10hardly enters the other track or the original track. As a result, it ispossible to suppress a detection error caused by reentrance of the lightray 10 reflected on the light non-transparent portion (the V-shapedprojection 8) into the other track or the original track.

The above discussion has been made on the case where it is constructedso that the incident light 4 entering one inclined surface 8 b should betotally reflected to enter the other inclined surface 8 a and should befurther totally reflected on the other inclined surface 8 a. Since theincident light is surely reflected totally on the light non-transparentportion (the inclined surfaces 8 a and 8 b) without being leaked on theside where the light detecting element 11 a is placed, this alsoproduces an effect of suppressing the stray light which is a cause oferror. Not only in the case where the incident light is totallyreflected on the other inclined surface 8 a, however, but also in thecase where at least part of the incident light is reflected on the otherinclined surface 8 a, similarly, with the construction where thereflected light 10 reflected on the other inclined surface 8 a shouldnot enter the light emitting portion and the reflecting portion (theelectrode of the light source 1 (light emitting element) and the die pad3) around the light emitting portion in the light source 1, it ispossible to suppress a detection error caused by the light ray reflectedon the light non-transparent portion (the V-shaped projection 8).

In a case where the light ray 4 enters the optical scale 7, beinginclined outward at an angle of φ with respect to the optical axis 6, inother words, in a case where an angle made by the normal of the flatsurface (the flat portion 9) and the optical axis 6 of the incidentlight 4 from the light source 1 is φ, Eq. (3) is changed as follows,like in the second preferred embodiment, where with respect to φ, thecounterclockwise direction is positive and the others are scalar.θ=|sin⁻¹(n sin(4α+φ))|  (3b)

Further, in all the cases or most cases of a representing the incidentposition of the light ray 4, α has only to be set as follows:(−45+θc−φ)/3<α<45−θc−φ (deg)  (5b)If φ≧−4α, in other words, α≧−φ/4 is satisfied, α is set so that theconditional expression obtained by substituting Eq. (3b) into Eq. (9)and 0<α<45 as well as Eq. (5b) should be satisfied.If φ<−4α, in other words, α<−φ/4 is satisfied, α is set so that theconditional expression obtained by substituting Eq. (3b) into Eq. (9b)and 0<α<45 as well as Eq. (5b) should be satisfied.a+L tan θ>D/2  (9b)

Though the above discussion in the fourth preferred embodiment has beenmade on the case where the light ray 4 going on the left side of theoptical axis 6 enters the left inclined surface 8 b of the V-shapedprojection 8, if the light ray 4 going on the right side of the opticalaxis 6 enters the right inclined surface 8 a of the V-shaped projection8, the phenomenon symmetrical to the above case occurs.

Further, if the light ray 4 going on the left side of the optical axis 6enters the right inclined surface 8 a of the V-shaped projection 8, α isset so that 0<α<45, the conditional expression obtained from Eqs. (3a)and (9b) and Eq. (5a) should be satisfied, where φ≦4α, in other words,α≧φ/4 is satisfied.

If φ>4α, in other words, α<φ/4 is satisfied, α is set so that 0<α<45,the conditional expression obtained from Eqs. (3a) and (9) and Eq. (5a)should be satisfied.

Further, though the above discussion in the fourth preferred embodimenthas been made on the case where the tilt angle of the inclined surfaces8 a and 8 b of the V-shaped projection 8 is (45−α) degrees with respectto the flat portion 9 (flat surface), also if the tilt angle of theinclined surfaces 8 a and 8 b of the V-shaped projection 8 is (45+α)degrees with respect to the flat portion 9 (flat surface), with the samemanner, α is set so that the reflected light 10 should not enteranywhere within the effective diameter D of the lens 5 within a range ofthe incident position a of the light ray 4 onto the optical scale 7.

Though the fourth preferred embodiment shows the respective ranges ofdesign values of α in the case where the light ray 4 enters the opticalscale 7, being inclined at an angle of φ with respect to the opticalaxis 6 and the light ray 4 enters the right inclined surface 8 a and theleft inclined surface 8 b, in an actual design, α is set so that bothconditional ranges of design values shown in the fourth preferredembodiment should be satisfied.

Needless to say, the optical scale 7 may be either a linear type shownin, e.g., FIG. 3 or a rotary type shown in, e.g., FIGS. 4 and 5.

The Fifth Preferred Embodiment

FIGS. 9A and 9B show a construction of an optical encoder in accordancewith the fifth preferred embodiment of the present invention, and FIG.9A is a cross section showing the whole construction and FIG. 9B is anenlarged cross section showing the vicinity of a trapezoidal projection(surrounded by a circle) of the construction shown in FIG. 9A.

While the V-shaped projections 8 or the V-shaped projections 12 are usedand the light ray 4 is reflected on the inclined surfaces 8 a and 8 b or12 a and 12 b in the first, second, third and fourth preferredembodiments, trapezoidal projections 13 are used and the light ray 4 isreflected on inclined surfaces 13 a and 13 b thereof in the fifthpreferred embodiment.

Also in the fifth preferred embodiment, like in the first, second, thirdand fourth preferred embodiments, a tilt angle of the inclined surfaces13 a and 13 b is (45−α) degrees or (45+α) degrees with respect to theflat portion 9 (flat surface) and α is set in the same manner as shownin the first, second, third and fourth preferred embodiments, andtherefore the reflected light 10 does not thereby enter the reflectionfilm such as the electrode or the die pad 3 of the light source 1. Alsoin this case, an angle made by the inclined surfaces 13 a and 13 b is(90+2α) degrees or (90−2α) degrees, i.e., (90+γ) degrees or (90−γ)degrees, where 0<γ<90.

FIG. 9 shows a case, as a typical example, where the tilt angle is(45−α) degrees with respect to the flat portion 9 (flat surface) and thelight ray 4 going on the left side of the optical axis 6 enters theright inclined surface 13 a of the trapezoidal projection 13.

As discussed above, in the fifth preferred embodiment, since it isconstructed so that the incident light 4 entering one inclined surface13 a (or inclined surface 13 b) should be totally reflected thereon toenter the other inclined surface 13 b (or inclined surface 13 a) andthen should be totally reflected on the other inclined surface 13 b (orinclined surface 13 a) and the reflected light 10 reflected on the otherinclined surface 13 b (or inclined surface 13 a) should not enter thelight emitting portion and the reflecting portion (such as the electrodeof the light source 1 (light emitting element) or the die pad 3) aroundthe light emitting portion in the light source 1, and the light ray 10reflected on the light non-transparent portion (the inclined surface 13a or 13 b of the trapezoidal projection 13) in one track on the opticalscale 7 does not enter the reflecting portion such as the electrode orthe die pad 3 in the light source 1 but is absorbed or scatteredtherein, the light ray 10 hardly enters the other track or the originaltrack. As a result, it is possible to suppress a detection error causedby reentrance of the light ray 10 reflected on the light non-transparentportion (the inclined surface 13 a or 13 b of the trapezoidal projection13) into the other track or the original track.

The above discussion has been made on the case where it is constructedso that the incident light 4 entering one inclined surface 13 a (orinclined surface 13 b) should be totally reflected to enter the otherinclined surface 13 b (or inclined surface 13 a) and should be furthertotally reflected on the other inclined surface 13 b (or inclinedsurface 13 a). Since the incident light is surely reflected totally onthe light non-transparent portion (the inclined surfaces 13 a and 13 b)without being leaked on the side where the light detecting element 11 ais placed, this also produces an effect of suppressing the stray lightwhich is a cause of error. Not only in the case where the incident lightis totally reflected on the other inclined surface 13 b (or inclinedsurface 13 a), however, but also in the case where at least part of theincident light is reflected on the other inclined surface 13 b (orinclined surface 13 a), similarly, with the construction where thereflected light 10 reflected on the other inclined surface 13 b (orinclined surface 13 a) should not enter the light emitting portion andthe reflecting portion (the electrode of the light source 1 (lightemitting element) and the die pad 3) around the light emitting portionin the light source 1, it is possible to suppress a detection errorcaused by the light ray 10 reflected on the light non-transparentportion (the inclined surface 13 a or 13 b of the trapezoidal projection13).

In a case where the light ray 4 enters the optical scale 7, beinginclined outward at an angle of φ with respect to the optical axis 6, inother words, in a case where an angle made by the normal of the flatsurface (the flat portion 9) and the optical axis 6 of the incidentlight 4 from the light source 1 is φ, Eq. (3) is changed into Eq. (3a)or (3b) and Eq. (5) is changed into Eq. (5a), (5b), (5c) or (5d), likein the first, second, third and fourth preferred embodiments.

Needless to say, the optical scale 7 may be either a linear type shownin, e.g., FIGS. 3A, 3B or a rotary type shown in, e.g., FIGS. 4A, 4B and5A, 5B.

The Sixth Preferred Embodiment

FIGS. 10A and 10B show a construction of an optical encoder inaccordance with the sixth preferred embodiment of the present invention,and FIG. 10A is a cross section showing the whole construction and FIG.10B is an enlarged cross section showing the vicinity of the trapezoidalprojection (surrounded by a circle) of the construction shown in FIG.10A.

While the optical scale 7 is constituted of the trapezoidal projections13 and the flat portions 9 which are alternately arranged in the fifthpreferred embodiment, no flat portion 9 is provided and the trapezoidalprojections 13 are continuously arranged and an upper base (flatsurface) 13 c functions as light transmission portion in the sixthpreferred embodiment.

Also in the sixth preferred embodiment, like in the fifth preferredembodiment, the tilt angle of the inclined surfaces 13 a and 13 b is(45−α) degrees or (45+α) degrees with respect to the upper base (flatsurface) 13 c and α is set in the same manner as shown in the first,second, third and fourth preferred embodiments, and therefore thereflected light 10 does not thereby enter the reflection film such asthe electrode or the die pad 3 of the light source 1. Also in this case,the angle made by the inclined surfaces 13 a and 13 b is (90+2α) degreesor (90−2α) degrees, i.e., (90+γ) degrees or (90−γ) degrees, where0<γ<90.

FIG. 10B shows a case, as a typical example, where the tilt angle is(45−α) degrees and the light ray 4 going on the left side of the opticalaxis 6 enters the right inclined surface 13 a of the trapezoidalprojection 13.

As discussed above, in the sixth preferred embodiment, since it isconstructed so that the incident light 4 entering one inclined surface13 a (or inclined surface 13 b) should be totally reflected thereon toenter the other inclined surface 13 b (or inclined surface 13 a) andthen should be totally reflected on the other inclined surface 13 b (orinclined surface 13 a) and the reflected light 10 reflected on the otherinclined surface 13 b (or inclined surface 13 a) should not enter thelight emitting portion and the reflecting portion (such as the electrodeof the light source 1 (light emitting element) or the die pad 3) aroundthe light emitting portion in the light source 1, and the light ray 10reflected on the light non-transparent portion (the inclined surface 13a or 13 b of the trapezoidal projection 13) in one track on the opticalscale 7 does not enter the reflecting portion such as the electrode orthe die pad 3 in the light source 1 but is absorbed or scatteredtherein, the light ray 10 hardly enters the other track or the originaltrack. As a result, it is possible to suppress a detection error causedby reentrance of the light ray 10 reflected on the light non-transparentportion (the inclined surface 13 a or 13 b of the trapezoidal projection13) into the other track or the original track.

The above discussion has been made on the case where it is constructedso that the incident light 4 entering one inclined surface 13 a (orinclined surface 13 b) should be totally reflected to enter the otherinclined surface 13 b (or inclined surface 13 a) and should be furthertotally reflected on the other inclined surface 13 b (or inclinedsurface 13 a). Since the incident light is surely reflected totally onthe light non-transparent portion (the inclined surfaces 13 a and 13 b)without being leaked on the side where the light detecting element 11 ais placed, this also produces an effect of suppressing the stray lightwhich is a cause of error. Not only in the case where the incident lightis totally reflected on the other inclined surface 13 b (or inclinedsurface 13 a), however, but also in the case where at least part of theincident light is reflected on the other inclined surface 13 b (orinclined surface 13 a), similarly, with the construction where thereflected light 10 reflected on the other inclined surface 13 b (orinclined surface 13 a) should not enter the light emitting portion andthe reflecting portion (the electrode of the light source 1 (lightemitting element) and the die pad 3) around the light emitting portionin the light source 1, it is possible to suppress a detection errorcaused by the light ray 10 reflected on the light non-transparentportion (the inclined surface 13 a or 13 b of the trapezoidal projection13).

In a case where the light ray 4 enters the optical scale 7, beinginclined outward at an angle of φ with respect to the optical axis 6, inother words, in a case where an angle made by the normal of the flatsurface (the upper base 13 c) and the optical axis 6 of the incidentlight 4 from the light source 1 is φ, Eq. (3) is changed into Eq. (3a)or (3b) and Eq. (5) is changed into Eq. (5a), (5b), (5c) or (5d), likein the first, second, third and fourth preferred embodiments.

Needless to say, the optical scale 7 may be either a linear type shownin, e.g., FIGS. 3A, 3B or a rotary type shown in, e.g., FIGS. 4A, 4B and5A, 5B.

The Seventh Preferred Embodiment

In the above preferred embodiments, discussion has been made on the casewhere the tilt angles of the two inclined surfaces are the same in theoptical scale comprising the light non-transparent portion consisting ofat least one pair of inclined surfaces which are opposed in such amanner as to become farther away from each other towards the side wherethe incident light enters. The tilt angles of the two inclined surfaces,however, may be different from each other.

Hereinafter, discussion will be made on the case where the tilt anglesof the two inclined surfaces 8 a and 8 b are different from each otherin the optical scale of the first preferred embodiment, and the sameapplies to any optical encoder shown in the second to sixth preferredembodiments.

In FIG. 2, for example, the tilt angle of one inclined surface 8 a withrespect to the flat portion 9 (flat surface) is (45−α) degrees and thatof the other inclined surface 8 b is (45−β) degrees, whereα≠β0<α<450<β<45and the refractive index of the optical scale 7 is selected so that thecritical angle θc which depends on the difference in refractive indexbetween it and a peripheral portion such as air should be;θc<45−αθc<45−β

The angle made by the inclined surfaces 8 a and 8 b is (90+α+β) degrees,i.e., (90+γ) degrees, where 0<γ<90.

The reflected light 10 is reflected twice in the V-shaped projection 8and after the angle made by the optical axis 6 of the incident light 4and the reflected light 10 becomes θ, the reflected light 10 isrefracted again by the lens 5 and reaches the light source portion(substrate 2), but in the optical encoder of the seventh preferredembodiment, α and β are set so that the reflected light 10 should enterthe substrate 2 at a position outside the die pad 3 (the reflected light10 should not enter the light emitting portion and the reflectingportion such as the die pad 3 or the electrode around the light emittingportion in the light source 1), in other words,x>w  (1)should be satisfied, where x represents a distance between the incidentposition of the reflected light 10 onto the substrate 2 and the lightemitting point of the light source 1 and w represents a distance betweenan end of the die pad 3 and the light emitting point of the light source1.

Therefore, the seventh preferred embodiment can produce the same effectas that of the first preferred embodiment.

Though it is assumed in the seventh preferred embodiment that thesubstrate 2 has a surface in which light is absorbed or scattered andvery few light is regularly reflected, however, if the substrate 2 has ahigh rate of regular reflection like the die pad 3, the above referencesign w represents a distance between an end of a region having a highrate of regular reflection and the light emitting point of the lightsource 1 instead.

Also in the case where an angle made by the normal of the flat surface(the flat portion 9) and the optical axis 6 of the incident light 4 fromthe light source 1 is φ, though detailed discussion is omitted, it isobvious that the same effect as that in the first preferred embodimentcan be produced even if the tilt angles of the two inclined surfaces 8 aand 8 b are different from each other.

Further, when the angle made by the inclined surfaces 8 a and 8 b is(90+γ) degrees, in other words, out of 90 degrees, since the reflectedlight 10 is not parallel with the incident light 4, in the case where atleast one of the inclined surfaces 8 a and 8 b (e.g., the inclinedsurface 8 a) is inclined at an angle of (45−α) degrees or (45+α) degreeswith respect to the flat surface and the other inclined surface (e.g.,the inclined surface 8 b) is inclined at an angle of 45 degrees withrespect to the flat surface, or also in the case where one inclinedsurface (e.g., the inclined surface 8 a) is inclined at an angle of(45−α) degrees with respect to the flat surface and the other inclinedsurface (e.g., the inclined surface 8 b) is inclined at an angle of(45+β) degrees with respect to the flat surface, by appropriatelysetting the values of α and β, the construction can be achieved wherethe incident light entering one inclined surface (any one of theinclined surfaces 8 a and 8 b) is totally reflected thereon to enter theother inclined surface and at least part of the light is reflected onthe other inclined surface and the reflected light 10 reflected on theother inclined surface does not enter the light emitting portion and thereflecting portion (the electrode of the light source 1 (light emittingelement) or the die pad 3) around the light emitting portion in thelight source 1.

The Eighth Preferred Embodiment

FIG. 11 shows a principal part of an optical encoder in accordance withthe eighth preferred embodiment of the present invention, morespecifically, is a plan view where the light source portion is viewedfrom the side of the optical scale.

In general, an electrode 19 is provided on the light source 1 such as anLED or a surface emitting laser diode and supplied with a drivingcurrent through a metal wire 21, and a light emitting point 20 emitslight. The light source 1 is placed on the die pad 3 on the substrate 2.

Since a metal is generally used as an material of the electrode 19 andthe die pad 3 and its reflectance is high as discussed in the firstpreferred embodiment, the reflected light 10 from the optical scale 7 isreflected again on the electrode 19 or the die pad 3 and this causes theproblem in the background art.

In the eighth preferred embodiment, an anti-reflection film 22 (in FIG.11, for easy understanding, a grid mesh is given), such as a blackresist film, which functions to reduce the reflectance is provided onthe electrode 19 and the die pad 3. The anti-reflection film 22,however, is not provided near a junction portion between the electrode19 and the metal wire 21 in order to keep electrical conduction.

The black resist film can be formed as the anti-reflection film 22 witha desired size at a desired position, for example, by applying a blackresist through spin coat processing or the like onto a portion on awafer before dicing, on which a plurality of LEDs are formed, other thanthe light emitting point, placing a mask with a light shielding portionagainst exposure light beams, with the same size at the same position asthose of the desired anti-reflection film, exposing the wafer anddeveloping it. Likewise, the anti-reflection film 22 can be formed alsoon the substrate 2.

Such an anti-reflection film 22 can be formed, for example, after thelight source 1 provided with the electrode 19 is joined onto the die pad3 on the substrate 2 and the metal wire 21 is joined to the electrode19. For example, black ink or the like which is to become theanti-reflection film 22 has only to be applied manually or with a robot.Further, in this case, if the anti-reflection film 22 having theelectrical insulation property is used, the portion near the junctionportion between the electrode 19 and the metal wire 21 can be alsocovered with the anti-reflection film 22.

As discussed above, in the eighth preferred embodiment, since at leastpart of the reflecting portion (the electrode 19 of the light source 1and the die pad 3) around the light emitting portion of the light source1 is covered with the anti-reflection film, even if the reflected lightreflected on the light non-transparent portion in one track on theoptical scale enters the reflecting portion (the electrode 19 and thedie pad 3 of the light source 1) around the light emitting portion ofthe light source 1, most of the reflected light is absorbed by theanti-reflection film 22 and the reflected light hardly reenters theother track or the original track. As a result, it is possible tosuppress a detection error caused by reentrance of the light rayreflected on the light non-transparent portion into the other track orthe original track.

The anti-reflection film 22 on the die pad 3 may cover not only the diepad 3 but also the entire substrate 2.

Needless to say, the optical scale 7 may be either a linear type shownin, e.g., FIGS. 3A, 3B or a rotary type shown in, e.g., FIGS. 4A, 4B and5A, 5B.

The eighth preferred embodiment may be performed alone and may beperformed together with any one of the first to seventh preferredembodiments at the same time.

When the eighth preferred embodiment is performed alone, this can beapplied to not only the case where the light non-transparent portion isconstituted of the inclined surfaces but also a case where the lightnon-transparent portion is formed of an opaque portion such as achromium layer formed on a transparent substrate such as a glass, andthis can suppress an error caused by reentrance of a light ray reflectedon the opaque portion such as a chromium layer into an other track orthe original track. In order to manufacture the optical scale includingthe light non-transparent portion formed of the opaque portion, a methodof making a slit by etching a metal plate or the like can be used.

The Ninth Preferred Embodiment

FIG. 12 shows a principal part of an optical encoder in accordance withthe ninth preferred embodiment of the present invention, morespecifically, is a plan view where the light source portion is viewedfrom the side of the optical scale.

In general, the electrode 19 on the light source 1 such as an LED or asurface emitting laser diode has an area which is sufficiently largerthan a contact area between it and the metal wire 21, and the die pad 3has an area which is several times as large as a contact area between itand the light source 1.

In the ninth preferred embodiment, the areas of the electrode 19 and thedie pad 3 are made as small as possible, to become almost equal to therequired contact areas with the metal wire 21 and the light source 1,respectively, and an area of the reflecting portion is thereby reduced.

Therefore, the probability that the light ray reflected on the lightnon-transparent portion in one track on the optical scale should enterthe reflecting portion such as the electrode 19 and the die pad 3 of thelight source 1 (around the light emitting portion of the light source 1)becomes lower and the reflected light hardly enters the other track orthe original track. As a result, it is possible to suppress a detectionerror caused by reentrance of the light ray reflected on the lightnon-transparent portion into the other track or the original track.

Further, it is preferable that the area of the die pad 3 should be madelarger, uniformly from the periphery of a contact face of the lightsource 1 with the die pad 3 so as to be larger than the contact area ofthe light source 1 with the die pad 3. The size is within 100 μm fromthe periphery of the contact face of the light source 1 with the die pad3, preferably within 50 μm, and further preferably within 10 μm.

The area of the die pad 3, however, may be equal to the area of thecontact face of the light source 1 with the die pad 3 or smaller.

With respect to the electrode 19, though a specific value is hard todefine, it may be provided only on one side of the light emitting point20, not entirely on the light source 1, as shown in FIG. 12.

Both the areas of the electrode 19 and the die pad 3 do not have to bemade as small as possible, and a reasonable effect can be produced byreducing at least either of them, for example, by making only the areaof the die pad 3 almost equal to the contact area with the light source1.

Needless to say, the optical scale 7 may be either a linear type shownin, e.g., FIGS. 3A, 3B or a rotary type shown in, e.g., FIGS. 4A, 4B and5A, 5B.

The ninth preferred embodiment may be performed alone and may beperformed together with any one of the first to eighth preferredembodiments at the same time.

When the ninth preferred embodiment is not performed together with anyone of the first to seventh preferred embodiments at the same time, thiscan be applied to not only the case where the light non-transparentportion is constituted of the inclined surfaces but also the case wherethe light non-transparent portion is formed of the opaque portion suchas a chromium layer formed on a transparent substrate such as a glass,and this can suppress an error caused by reentrance of a light rayreflected on the opaque portion such as a chromium layer into an othertrack or the original track.

The Tenth Preferred Embodiment

FIGS. 13 and 14A, 14B each show a construction of an optical encoder inaccordance with the tenth preferred embodiment of the present invention,and FIG. 13 is a cross section, FIG. 14A is a plan view viewed from thelight detecting portion and FIG. 14B is an enlarged plan view showingpart (surrounded by a circle) of the construction shown in FIG. 14A.

In the tenth preferred embodiment, it is constructed that a portion ofthe optical scale 7 which has no track is placed at a positionsymmetrical to the light non-transparent portion (e.g., the V-shapedprojection 8) within an irradiation region of the light ray (incidentlight) from the light source 1 with respect to the optical axis 6 of thelight source 1 as a symmetry axis.

A light ray 23 emitted from the light source 1 is reflected on the lightnon-transparent portion in a track 14 to become a reflected light 24 andreflected again on the reflecting portion (e.g., an electrode (notshown) on the light source 1) around the light emitting portion in thelight source 1 to reenter the optical scale 7, but the position wherethe reflected light 24 enters has no track and therefore the reentrancedoes not cause an error. Also in another track 15, likewise, a light ray25 emitted from the light source 1 is reflected on the lightnon-transparent portion in the track 15 to become a reflected light 26and reflected again on the reflecting portion (e.g., the electrode onthe light source 1) around the light emitting portion in the lightsource 1 to reenter the optical scale 7, but the position where thereflected light 26 enters has no track and therefore the reentrance doesnot cause an error.

Thus, in the tenth preferred embodiment, since it is constructed that aportion of the optical scale 7 which does not have the track 14 or 15 isplaced at a position symmetrical to the light non-transparent portionwithin the irradiation region of the light ray from the light source 1with respect to the optical axis 6 of the light source 1 as a symmetryaxis, even if the light ray 24 reflected on the light non-transparentportion in one track (e.g., the track 14) on the optical scale 7 isreflected again on the reflecting portion (such as the electrode and thedie pad 3) around the light emitting portion in the light source 1 toreenter the optical scale, the light ray hardly enters the other track(e.g., the track 15) or the original track (e.g., the track 14). As aresult, it is possible to suppress a detection error caused byreentrance of the light rays 24 and 26 reflected on the lightnon-transparent portion into the other track or the original track.

Though FIGS. 14A and 14B show the case where the optical scale 7 is arotary type and the top of the V-shaped projection 8 is extended along adirection of the radius of the optical scale 7, the tenth preferredembodiment is not limited to this case but may be a case where the topof the V-shaped projection 8 is extended to be parallel with thetraveling direction of the optical scale 7 as shown in, e.g., FIG. 5B,and needless to say, the optical scale 7 may be a linear type shown in,e.g., FIGS. 3A and 3B.

The tenth preferred embodiment may be performed alone and may beperformed together with any one of the first to ninth preferredembodiments at the same time.

When the tenth preferred embodiment is not performed together with anyone of the first to seventh preferred embodiments at the same time, thiscan be applied to not only the case where the light non-transparentportion is constituted of the inclined surfaces but also the case wherethe light non-transparent portion is formed of the opaque portion suchas a chromium layer formed on a transparent substrate such as a glass,and this can suppress an error caused by reentrance of the light rayreflected on the opaque portion such as a chromium layer into the othertrack or the original track.

1. An optical encoder comprising: an optical scale including a lighttransmission portion having a flat surface and a light non-transparentportion having inclined surfaces, and producing an output pattern basedon incident light, the output pattern functioning as an optical code; alight source portion including at least one light source for emittingthe incident light; and a light detecting portion including at least onelight detecting element for detecting the output pattern, wherein saidlight source portion faces said light detecting portion and said opticalscale is interposed between said light source portion and said lightdetecting portion, said light non-transparent portion includes at leastone pair of first and second inclined surfaces which are opposite eachother and become farther apart from each other towards said light sourceportion, where the incident light enters said light non-transparentportion, and inclined so that an incident angle of the incident lightfrom said light source on said first and second inclined surfaces is notsmaller than critical angle of incidence, and the incident lightincident on said first of said inclined surfaces is totally reflected bysaid first inclined surface and is incident on said second inclinedsurface so that at least part of incident light is reflected from saidsecond inclined surface, and reflected light, which is reflected fromsaid second inclined surface, does not enter a light emitting portion ofsaid light source and does not enter a reflecting portion disposedaround said light emitting portion.
 2. The optical encoder according toclaim 1, wherein an angle formed by said first and second inclinedsurfaces is (90+γ) degrees or (90−γ) degrees, where 0<γ<90.
 3. Theoptical encoder according to claim 2, wherein at least one of said firstand second inclined surfaces is inclined with respect to said flatsurface at (45−α) degrees or (45+α) degrees, where 0<α<45.
 4. Theoptical encoder according to claim 1, wherein, in said lightnon-transparent portion, the incident light which is incident on one ofsaid first and second inclined surfaces is totally reflected and isincident on the other of said first and second inclined surfaces and istotally reflected from said other of said first and second inclinedsurfaces.
 5. The optical encoder according to claim 3, wherein α is in arange from 1.15 degrees to 3 degrees.
 6. The optical encoder accordingto claim 3, wherein α is in a range from 0.76 degrees to 3 degrees. 7.The optical encoder according to claim 3, wherein α is in a range from1.91 degrees to 3 degrees.